In the filtering of various types of liquids in chemical plants, pulp mills, refineries or similar plants, it is common to use a filtering system involving a plurality of individual filter units positioned close together and provided with automatic control means for effecting backwashing. In the course of normal operation of said backwashing control means, same often becomes for one reason or another progressively less efficient, or may even suffer complete breakdown, and when this happens the filter unit to which such control means is connected fails to backwash properly. Where the filter is one of a group thereof, such breakdown is often not noticed immediately and the improper operation may continue for a substantial period of time before discovery.
One particular example of such problem occurs where the filters are handling liquid at an elevated temperature, often of the order of 400.degree.-550.degree.F. in frequently encountered refinery usages, and hence the filter housings and conduits associated therewith are heated to such levels and radiate heat accordingly. In presently standard constructions, the backwash controlling valves and actuators therefor are positioned closely adjacent, often between, the filter unit components, such as between the filter housings and the associated conduits, and are accordingly subjected to such radiated heat. Where, as is usual, the actuators are pneumatic, they utilize pistons with sealing means therein which sealing means are elastomeric and usually subject to rapid deterioration when subjected to temperatures as above mentioned, especially for prolonged periods. Thus, under normal operating conditions of such filters, these seals may, and often do, rapidly deteriorate. This may in some circumstances result merely in the loss of power needed to fully shift the valve but in other cases it can result in binding of the actuator piston and a consequent complete failure to effect backwashing. In such cases, even though the replacement of a piston seal, usually a simple O-ring, is of itself a relatively minor and inexpensive job, the heat to which the filters and conduits are subjected as above stated requires substantial cooling of the unit before a workman can under existing safety regulations approach same for repair and/or replacement of the defective mechanism. Since it may often take from 8 to 10 hours for the filter and system to which it is connected to cool sufficiently to permit such access by workmen, it is apparent that a relatively minor repair job can keep the filters and thereby often an entire processing line inactive for a considerable period of time. This is obviously costly and it has long been recognized as a disadvantage of the equipment available up to the present.
In certain types of otherwise highly satisfactory equipment the problem has been particularly acute in that the filter units are placed in at least two rows, each row being on opposite sides of a central header and the valves being directly above and/or below such central header. Such positioning of the valves places the controllers between and somewhat behind the filter units and this, while operationally convenient, makes same difficult of access for repair and/or replacement regardless of temperature considerations. However, when the equipment is hot as above outlined, such access becomes even more difficult and the cooling above mentioned must be substantial.
The problem is further intensified where a heat retaining box is placed around the filter unit but such box is nevertheless often used for heat conservation reasons.
Thus, since the filters are necessary to the systems in which they are used and no solution was known to the problem of actuator repair as above described, said problem and the difficulties arising therefrom have been tolerated.
Some attempts have been made to obtain the benefits of such heat retaining box without the damage above mentioned arising from overheating of the actuators by wrapping insulative material around the conduits and valves and, if desired, even around the filter units but leaving the actuators projecting therefrom. This works reasonably well and is hence often used in place of the heat retaining box. This, however, generates substantial expense in both the original application of said insulative material and in the maintenance thereof. Further, where such insulative wrapping is used it renders all parts difficult of access and hence creates further expense in the proper maintenance of the equipment.
Other attempts to meet this problem have involved wrapping the actuators with insulative material in order to protect them from the heat of the adjacent filters and conduits, particularly if said latter remain unwrapped. This, however, is likewise undesirable for the same reasons as above set forth, namely expense of wrapping, inconvenience and expense in maintenance, said latter particularly including the inconvenience and expense of obtaining access to the actuators for repair or maintenance thereof.
A still further suggestion for meeting the foregoing outlined problems has been to replace the normally used actuators by other control devices which would be capable of withstanding high temperature operating conditions. However, this is often not economically desirable or commercially available. Instead the normally used actuators are inexpensive and, excepting for the problems created by high temperature operating conditions as above outlined, are reliable in operation and simple to repair when needed.
Therefore, again, in spite of the problems above-described, the necessity of the filters in question to numerous industrial systems has impelled the continued use of such actuators and for lack of apparent solution said problems and resulting difficulties have been tolerated for several years.
Accordingly, the major objects of the invention include:
1. To provide an organizational pattern for a filter assembly which will maintain the effectiveness of currently known filter assemblies but which will permit the actuators for the backwash controlling valves to be placed in an accessible position for service and/or replacement regardless of whether the filter unit operates at an elevated temperature and regardless of the cause of the need for such service and/or replacement.
2. To provide apparatus, as aforesaid, in which, where the filter operates at an elevated temperature, the placement of said valve actuators can be outside of the heated zone surrounding the filter unit and the associated conduits.
3. To provide apparatus, as aforesaid, wherein such improved accessibility of the valves will not involve extended or complex mechanical linkage between the actuator and the valve.
4. To provide apparatus, as aforesaid, which will be particularly adaptable to the use of air energized valve actuators.
5. To provide apparatus, as aforesaid, which will not materially, if at all, increase the manufacturing cost of a filter assembly over that previously experienced.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.